Ignition device



y 0, 1967 HANS-CHRISTOF KLEIN 3,322,989

IGNITION DEVICE Filed NOV. 27, 1963 2 sheets s'heet l T I T I we??? L T il a Fig,2

Q2 INVENTOR.

HANS-CHRISTOF KLEIN May 30, 1967 HANS-CHRISTOF KLEIN 3,322,989

IGNITION DEVICE 2 Sheets-Sheet 2 Filed NOV. 27, 1963 26 HANS-CHRISTOF KLEIN INVENTOR.

United States Patent 3,322,989 IGNITION DEVICE Hans-Christof Klein, Hattersheim am Main, Germany,

assignor to Alfred Teves Maschinenund Armaturenfabrik KG, Frankfurt am Main, Germany, a corporation of Germany Filed Nov. 27, 1963, Ser. No. 326,616

Claims priority, application Germany, Nov. 28, 1962,

7 Claims. (Cl. 313-54) The present invention relates to ignition and like devices adapted to develop an interrupted or sustained electrical discharge through an interelectrode gap containing a fluid.

The use of electrical discharge to ignite combustible fluids (e.g. gaseous fuel-and-air mixtures, liquid fuels atomized or vaporized in admixture with air, and other combustion-sustaining fluids) is well knOWn and finds application in the automotive industry as well as in domestic and industrial burners and similar apparatus. For the most part, ignition devices of this type include a pair of spaced-apart electrodes between which there is established an electrode gap for the creation of a spark or arc adapted to ignite the fluid passing through this gap. In internalcombustion engines, for example, the ignition device can be a spark plug having a central electrode operating in conjunction with a counterelectrode formed on the housing of the spark plug, a gap of several mils being established between these electrodes. In other devices, the electrodes may be similar and juxtaposed with one another across a relatively large gap through which the combustible fluids pass. Thus, in so-called oil burners and the like, atomized liquid fuel is admixed with an air stream and forced through the mouth of the burner, a pair of electrodes extending into this stream to define the spark or are gap. When ignition devices are referred to herein, it is intended to include devices of both the spark-plug type and those adapted to promote interrupted or sustained electrical discharge in an electrode gap in the presence of moving combustible fluids.

For the most part, the efficiency of combustion in the region of the ignition device is a function of the fatness or intensity of the spark discharge. The latter is a measure of the dimension of the park, the longer or denser discharges being characterized as fat. Heretofore it has been the practice to increase the intensity of the electrical discharge in ignition devices of the type described above by increasing the discharge voltage or increasing the distance between the electrodes and, therefore, the length of the spark. The former method has been found to be relatively ineffective since there is a practical limit to the size of the spark with a given spark gap and this limit is readily reached. The second technique results in a substantial increase in the voltage drop across the electrodes, as a consequence of the augmented air path across which the spark must be developed. This increased air path, while advantageous once the spark has been developed, renders it almost impossible to produce a satisfactory spark with equipment operating at conventional voltages.

It is, therefore, the principal object of the present invention to provide an ignition device whereby the advantages of an increased interelectrode gap can be obtained Without, however, materially increasing the voltage that must be supplied to the electrodes to produce the discharge.

A further object of this invention is to provide a method of igniting combustible fluids with the aid of spark discharge wherein the aforementioned disadvantages of earlier techniques can be avoided.

Still another object of my invention is to provide an electrode system adapted to initiate spark discharge at relatively loW voltages.

Yet another object of the present invention is to provide a system for the ignition of large volumes of combustible gases with a relatively small ignition or detonation time and a correspondingly fast response.

These objects and others which will become apparent hereafter are attained, in accordance with the present in vention, by disposing a pair of spaced electrodes within a combustible gas at a spacing such that the voltage applied to the electrodes to produce spark discharge is normally ineffective to develop an arc across the electrodes, and preionizing the gas in the region of this gap by subjecting it to irradiation from a radioactive source advantageously located in the region of the ignition device. The ionization produced by the radioactive source lowers the resistance in the interelectrode gap to a level sufficient to promote electrical discharge at the indicated voltage supplied to the electrodes. In this matter it is possible to produce long spark discharges across spark gaps which would normally be excessively long and incapable of sustaining such charges, the preionization of the gas reducing the resistance of the spark gap to the equivalent of the resistance of a narrow gap in the absence of a radioactive source.

According to a more specific feature of this invention, the radioactive source is incorporated directly within the ignition device and is disposed in the region of one of the electrodes thereof. Thus, one or both electrodes can be composed of a central electrode member or core which extends into the combustion chamber and an insulating mass surrounding this member and interposed between it and the enveloping shelf. The radioactive composition is then incorporated directly in the insulating mass which can be a sintered ceramic body in the manner of the refractory insulating masses of automotive spark plugs and the electrodes of industrial burners. In this case, the radioactive composition can itself be refractory and capable of being sintered into the enveloping body of ceramic material.

In accordance with a further aspect of this invention, the central or core member of the electrode system can include a transverse flange or plate axially spaced from the spark gap and adapted to receive the radioactive material, thereby positioning this material coaxially with respect to the central member and insuring a concentrated radioemission at the spark gap. The flange or plate can shield the exterior of the combustion chamber from undesirable radioactive emission. The radioactive composition can then be enclosed within a metallic shell or casing of annular configuration so that it fits around the central member and is seated against the flange, this metallic casing being sintered to the ceramic insulating body when the latter is aflixed to the central core and sintered to coherency. I have found that, although considerable advantage is gained by having only one of the electrodes associated with the radioactive composition, best results for the ignition of large volumes of combustible gas are obtained when the juxtaposed electrodes both contain the radioactive composition so that a uniform zone of preionized gas is produced in the region of both electrodes. While substantially any source of ionizing radiation can be employed in conjunction with the instant invention, it should be noted that compositions which are essentially 'y emitters should be avoided since 7 radiation cannot be effectively contained within the combustion chamber and may result in an environmental irradiation of a highly undesirable type. On the other hand, a-particle emitters are satisfactory since they produce a large number of ion pairs per emission. Since a particles are readily absorbed, however, their incorporation in the ceramic mass frequently results in a reduction in the aradiation intensity within the combustion chamber. Those substances which are principally or emitters are generally also 'y-ray sources either directly or indirectly. Under these circumstances, fi-particle emitters are best employed in accordance with the present invention. It is also contemplated to provide, in the region of the radioactive composition, a substance capable of undergoing nuclear transformation, i.e. on or ,8 emission, upon irradiation by the radioactive material. When the term radioactive is used herein, it is meant to designate those substances which exist in Nature in a radioactive state as well as those synthetically produced isotopes having relatively long half-lives (e.g. in excess of one year) since shorter half-lives are impractical for devices having long useful lives.

The above and other objects, advantages and features of the present invention will become more readily apparent from the following description, reference being made to the appended drawing is which:

FIG. 1 is an axial cross-sectional view through a combustion chamber provided with a pair of ignition devices in accordance with the present invention;

FIG. 2 is an axial cross-sectional view of a fragment of one of the ignition devices; and

FIG. 3 is an axial cross-sectional view through an automotive spark plug embodying the invention.

In FIGS. 1 and 2 I show an apparatus wherein a pair of juxtaposed walls 3, 4 comprise a housing forming a combustion chamber 5, these walls having sleeve portion 3', 4' in which are received a pair of ignition devices 1, 2 to be described in greater detail hereinafter. The ignition devices have cylindrical shanks 1, 2 threaded into the walls 3, 4 and entrainable by a socket wrench at their hexagonal heads 1", 2" to seat annular shoulders 10, 2a against resiliently compressible metallic sealing rings 1b, 2b composed of a metal such as brass. From the nuts 1", 2", the ceramic insulating body 10, 20 of the ignition devices 1, 2 extends outwardly away from chamber 5 and terminates in conductive caps 10, 2c at which connection can be made to an external electric circuit providing the necessary current for the discharge. The caps 10, 2c thus constitute terminals for the central electrode members 6, 7 of each ignition device. The projecting portions of electrodes 6, 7 extend into the chamber 5 and define the spark gap 8 as indicated. When the ignition devices 1, 2 are provided with equivalent quantities of radioactive material, as illustrated in FIG. 2, and the radiation confined to the region of the gap 8, the gas within combustion chamber 5 is ionized in the axially symmetrical zone indicated at 9 by broken lines.

As indicated in FIG. 2, an ignition device 1 of the type shown in FIG. 1 comprises essentially a metallic shell or sleeve 17 in which a ceramic insulating body 10 is held by a frustoconical spring ring 16, seated against an annular shoulder 16 in the interior of sleeve 17. The insulating body 10 has a frustoconical portion 10' which centers it within the interior of the sleeve against a sealing ring which can be composed of a compressible metal such as brass or a heat-resistant elastomeric substance. The shank 11 of the central electrode 6 is embedded in the ceramic body 10 and can be sintered thereto. The projecting portion of electrode 6 is received within the hollow end 11 of shank 11 and is provided with an annular, forwardly concave transverse flange 13 constituting a backing plate for the radioactive composition 12 centered thereby around electrode 6. The radioactive material 12 is contained within a shell 14, composed of a sinterable metal such as titanium, and is coaxial with the stem 6 and separated from the chamber 5 by a relatively narrow partition 10", the remainder of the body in the region of the radioactive material having a thickness in excess of that of the partition 10" so as to serve as an absorber for spurious emission. Consequently all radioemission from the source 12 is concentrated at the spark gap in the zone illustrated at 9. It should be noted that the backing plate 13 functions in part as an absorber preventing emission rearwardly along the electrode 11 in the event that any fissures develop in the ceramic body 10 around the shank of the electrode, in part as a layer of material adapted to increase the backscattering of the emitted radiation and thus increase the ionization within chamber 5, and in part as a centering element holding the radioactive material 12 and its shell 14 in place during sintering.

While it is preferred to dispose the radioactive material uniformly in the region of both of the electrodes forming the spark or discharge gap in order to uniformly ionize the gas in the gap, under certain circumstances it is equally suitable to provide the radioactive material around only one of the electrodes; in any event, the use of the radioactive material serves to ionize the gas in the region of the electrode with which it is associated and thus reduces the resistance of the spark gap. In FIG. 3 I show an automotive spark plug 20 with an insulating body 21 surrounding a central elect-rode 22 whose terminal 23 connects this electrode to one side of the energizing source. The insulating body 21 is surrounded by a metal housing 24 whose shank 25 is threadedly receivable within a cylinder block in the usual manner and constitutes the terminal for a counterelectrode 26 juxtaposed with the projecting extremity 27 of the central electrode 22. Thus a spark gap 28 is provided between the two electrodes at a location axially spaced from a toroidal casing 29 surrounding the central electrode 22 and embedded in the ceramic insulating body 21, this casing 29 containing a radioactive material 30 as previously described. Electrode portion 27 is formed with an annular flange 31 constituting a backing plate as previously described with reference to FIG. 2. Except for the radioactive material 30, spark plug 20 is essentially similar to a conventional spark plug, it being noted that the use of a quantity of radioactive substance on the order of 1 microcurie can produce sufficient ionization in the region of the spark gap to enable the doubling of its size when conventional spark coils are used; the spark duration is similar to that of conventional spark plugs.

Because of the large number of ion pairs produced by a-particle emission, it may be desirable to employ as the radioactive substance one or more of the naturally occurring tar-particle sources. Most economical results are obtained with the elements of U decay chain, since this isotope is perhaps the most inexpensive of those tar-particle emitters, although the elements of this chain give rise to flor 'y-ray emission. It will be evident that 'y emitters should, for the most part, be avoided since this 7 radiation is essentially unshielded by the materials constituting the emission device and the walls of the combustion chamber. 5 emissions can be readily blocked from escaping from the combustion chamber by an increase in the wall thickness, if necessary, or by forming the partition 10 with such density that the mean-free path of a [3 particle emerging from the ignition device is less than the dimension of the chamber in the direction of the spark plug or ignition device and is not substantially greater than half this dimension when a pair of juxtaposed electrodes are provided. As a suitable particle emitter for the present purposes, I have found that the synthetically produced isotope Na, which has a half-life of three years and whose Q energy is such that between 50 and ions are produced per cm. of path length, is satisfactory. As previously mentioned, the radioactive composition can be sintered directly into the ceramic body or enclosed within the metal shell 14 or 29.

According to one example of the invention the radioactive isotope U and about 1 microcurie of this material in the form of the tetravalent uranium oxide (U0 is disposed in a mass of sinterable ceramic particles (i.e. aluminum oxide with a conventional resinous binder) and the entire mass sintered at a temperature of about 1450 C. to coherency. This is possible since the uranium oxide is essentially refractory and, indeed, has a melting point of 2227 C.

Similarly, an equivalent amount of the sodium isotope can be admixed with the ceramic particles as a refractory binder in the form of the silicate ('Na SiO Again, sintering of the particles, which can have a particle size of about 300 mesh, is carried out at 1450 C., the sodium silicate melting at 1027 C. and solidifying upon cooling to enhance the coherency of the ceramic body in the region of the radioactive material. The sodium isotope can be produced from Mg in the usual way and decays to the stable neon isotope Ne In order to ensure that the sodium silicate will remain concentrated in the region of the central electrode and not distribute itself throughout the ceramic body upon liquification, the radioactive material is enclosed within the shell 14, 29 which is composed of a refractory metal. In this case the shell can have a thickness of several mils and be composed of titanium which has a melting point of 1727 C. so that it can be sintered in place within the ceramic body Without deterioration. Since the specific gravity of the shell is about 4.4 grams/cm}, its B-particle absorption is not excessive. The sodium silicate can be introduced into the shell in its solid state and although it undergoes a change of shape and volume upon melting and substance solidification, it remains located in the "region of the central electrode as a consequence of the shape-retention capabilities of the metal shell.

The invention described and illustrated is believed to admit of many modifications within the ability of persons skilled in the art, all such modifications being considered within the spirit and scope of the appended claims.

What is claimed is:

1 A device for the ignition of combustible fluids comprising:

an elongated body of insulating material;

an electrode extending longitudinally through said body and projecting therebeyond at one extremity of said body for juxtaposition with a counterelectrode to generate an electrical discharge in the region of said extremity to ignite said fluid;

a radioemissive source imbedded in said body at said extremity for ionizing at least some of said fluid in the region of said discharge; and a metallic casing surrounding said electrode and receiving said radioemissive source, said casing being sinter-bonded to said body therewithin, said electrode being provided with a transverse radiation-absorbing annular flange spaced from said discharge extremity Within said body and disposed rearwardly of said radioemissive source with respect to said extremity, said casing being seated against said flange.

2. An ignition device as defined in claim 1 wherein said radioemissive source is a refractory material.

3. A device as defined in claim 1, further comprising a metallic shell surrounding said body.

4. A device as defined in claim 3, further comprising a counterelectrode mounted on said shell to form a discharge gap with said electrode.

5. A device for the ignition of combustible fluids, comprising:

an elongated body of a refractory insulating material;

an electrode extending longitudinally through said body 6 and projecting therebeyond at one extremity of said body for juxtaposition with a counterelectrode to generate an electric discharge in the region of said extremity to ignite said fluid; and

an annular mass of radioactive material wholly imbedded in said body and surrounding said electrode While being spaced from said extremity by a distance less than that at which said body absorbs a major part of the emissivity, said electrode having a transverse flange extending outwardly therefrom beyond said mass and between the latter and the other extremity of said electrode, said mass of radioactive material being seated substantially against said flange.

6. A device for the ignition of combustible fluids, comprising:

an elongated body of a refractory insulating material;

an electrode extending longitudinally through said body and projecting therebeyond at one extremity of said body for juxtaposition with a counterelectrode to generate an electric discharge in the region of said extremity to ignite said fluid; and

an annular mass of radioactive material wholly imbedded in said body and surrounding said electrode while being spaced from said ex-tremity by a distance less than that at which said body absorbs a major part of the emissivity; and

a toroidal metallic shell enclosing said mass and sintered to said body and said mass.

7. A device for the ignition of combustible fluids, comprising a pair of juxtaposed electrodes forming a discharge gap therebetween, respective ceramic bodies surrounding said electrodes with said electrodes projecting beyond respective discharge extremities of said bodies, respective radioemissive sources of equivalent ionizing capability embedded within said bodies at said extremities for ionization of substantially equal volumes of said fluid at said gap, a respective metallic casing surrounding each of said electrodes and receiving the respective radioemissive source, said casings being sinter-bonded to the respective bodies therewithin, each of said electrodes being provided with a respective transverse radiationabsorbing annular flange spaced from the respective discharge extremity Within each body and disposed rear- Wardly of the radioemissive source with respect to the resmctive discharge extremities, each of said casings being seated against the respective flange.

References Cited UNITED STATES PATENTS 1,275,020 8/1918 Harding 313-54 1,930,088 10/1933 Foulke 313-54 1,996,854 4/1935 Capart 313-54 2,128,408 8/1938 Gremier 313-54 2,221,519 11/1940 Jones et al. 158-1175 2,457,973 1/1949 Blau 313-54 2,472,720 6/1949 Nagel 158-1175 2,776,394 1/1957 Cuny et al. 317-96 2,894,315 7/ 1959 Candlize 29-25 .12 2,969,582 1/1961 Meredith et al 29-25.12 3,207,953 9/1965 Smith et a1 317-96 FOREIGN PATENTS 722,287 12/1931 France.

731,877 6/1932 France.

869,152 .5/ 1961 Great Britain.

RICHARD M. WOOD, Primary Examiner. V. Y. MAYEWSKY, Assistant Examiner. 

1. A DEVICE FOR IGNITION OF COMBUSTIBLE FLUIDS COMPRISING: AN ELONGATED BODY OF INSULATING MATERIAL; AN ELECTRODE EXTENDING LONGITUDINALLY THROUGH SAID BODY AND PROJECTING THEREBEYOND AT ONE EXTREMITY OF SAID BODY FOR JUXTAPOSITION WITH A COUNTERELECTRODE TO GENERATE AN ELECTRICAL DISCHARGE IN THE REGION OF SAID EXTREMITY TO IGNITE SAID FLUID; A RADIOEMISSIVE SOURCE IMBEDDED IN SAID BODY AT SAID EXTREMITY FOR IONIZING AT LEAST SOME OF SAID FLUID IN THE REGION OF SAID DISCHARGE; AND A METALLIC CASING SURROUNDING SAID ELECTRODE AND RECEIVING SAID RADIOEMISSIVE SOURCE, SAID CASING BEING SINTER-BONDED TO SAID BODY THEREWITHIN, SAID ELECTRODE BEING PROVIDED WITH A TRANSVERSE RADIATION-ABSORBING ANNULAR FLANGE SPACED FROM SAID DISCHARGE EXTREMITY WITHIN SAID BODY AND DISPOSED REARWARDLY OF SAID RADIOEMISSIVE SOURCE WITH RESPECT TO SAID EXTREMITY, SAID CASING BEING SEATED AGAINST SAID FLANGE. 